Abstract
To compare the two different anterior cruciate ligament surgery techniques’ effect in rehabilitation and activity performance. Fifty-five patients were evaluated. Twenty-seven patients with transtibial technique (TT), 28 with anatomic single-bundle technique (AT) included. Tegner Activity Scale (TAS) was performed at preoperation and follow-up. The returning time of the sport and work was evaluated at follow-up. Single-leg hop test was performed at follow-up. Outcomes were compared between the two groups. The determined length difference between the operated knee and the intact knee was compared between the two groups. Average age of TT and AT was 27.9±6.4 yr, 28.3±6 yr, respectively. There was a significant difference between the two groups in duration of returning to sport. TT group had higher duration to return to sport (P<0.01). No difference between the two groups in duration of returning to work (P>0.05). There was a significant difference between the two groups. TT group had significantly higher values than AT group (P<0.01). No difference in TAS between the two techniques at preoperation and at last follow-up (P>0.05). The increase of TAS in patients who had AT was higher than the patients who had TT (P>0.05). No difference in single-leg hop test at 55%–65%, 65%–75%, and 85%–95% level (P>0.05). In this test at 75%–85% TT group had higher values than AT group (P<0.05), AT group had higher values at 95%–105% level (P<0.05). Good short and long-term knee outcome scores depend on rehabilitation protocol after surgery. Surgery technique should provide the adequate stability in rehabilitation period. AT obtains better outcomes in rehabilitation.
Keywords: Anterior cruciate ligament, Anatomic single-bundle, Transtibial, Anterior cruciate ligament rehabilitation, Singe-leg hop test
INTRODUCTION
The anterior cruciate ligament (ACL) is a key knee stabilizer and its main function is to prevent anterior translation of the tibia on the femur. ACL injuries remain high in the athletic arena. Orthopaedic Sports Medicine has identified it as the single largest problem affecting the athletes (Woo et al., 2006). The anterior cruciate-deficient knee in many patients prevents successful return to sports and their best chance of doing so is by undergoing primary ACL reconstruction.
A study conducted by the National Football League during a 4-year period (1994–1998) indicates that an averaging 2,100 injuries were reported per year with knee injuries accounting for 20% of all injuries of which 2% were ACL injuries (Woo et al., 2006). ACL injury is a noncontact event which occurs more frequent in females than male athletes (Arendt and Dick, 1995; Hurd et al., 2008; Hutchinson and Ireland, 1995; Ireland, 1999).
The incidence of ACL injuries in sports is significantly higher during competition than training and this finding is consistent among all sports (Prodromos et al., 2007).
The main goals of ACL reconstruction are the reduction or elimination of knee instability, the restoration function lose, achieving the activity status before the injury and the prevention of long-term joint degeneration.
The localization of the femoral tunnel is particularly important in terms of isometric placement of the graft.
This study was done to compare the two different ACL surgery techniques’ effect in rehabilitation and activity performance.
MATERIALS AND METHODS
Ethical approval was obtained from the Institutional Review Board of Sisli Etfal Training and Research Hospital (approval number: 08/04/2014-630). Informed consent was obtained from all patients prior to participation in the study.
Taking into consideration of instability findings detected on physical examination, direct and indirect ACL insufficiency in magnetic resonance imaging, prior trauma activity level and desired future activity level, factors such as the presence of additional pathologies apart from ACL in the preoperative evaluation of the patients, reconstruction was decided. While deciding about the surgery time of patients who were applied early after the injury, edema in the knee and range of motion of the knee were evaluated in the first place. Furthermore, the social structure of the patient, activity level, occupation, the presence of inflammation, the adequacy of muscle strength were also considered.
In the study patients were advised to return to sports after having adequate hamstring and quadriceps strength, knee range of motion, stability and function as compared to the opposite unaffected knee and after successfully undergoing a phase of sports-specific training.
In our study, 55 patients who were applied ACL reconstruction surgery were evaluated. Among these patients who were applied arthroscopic ACL reconstruction surgery using the transtibial technique 27 patients with adequate follow-up of at least 12 months were enrolled in the study. On the other hand, patients who were performed arthroscopic ACL reconstruction surgery using anatomical single-bundle technique, 28 patients with adequate follow-up of at least 12 months were enrolled in the study.
The Tegner Activity Scale (TAS) is a subjective rating scale, which assessed the patient’s activity level before and after surgery. It comprises of eight knee symptoms of which each symptom has a range of function which the patient matches to their level of activity if the symptom occurred. The total score is graded as poor (<66), fair (66–83), good (84–90) and excellent (>90).
TAS was performed to the patients before the surgery and at last follow-up. The returning time of the sport and work was evaluated after surgery. Single-leg hope test was performed at last follow-up. Outcomes were compared between the two groups.
Each patient was laid in the supine position, knees at full extension and relaxed position prior to measurement of the circumference of the thigh muscles. Both thigh circumference were measured and recorded from 15 cm proximal to the upper limit of the patella for measuring. The determined length difference between there operated knee and the intact knee was recorded. Results were compared between the two groups.
Patients with combined ligament and meniscal injuries were excluded from the study. Same rehabilitation protocol was applied to all patients in the study.
NCSS 2007 and PASS 2008 Statistical Software (Kaysville, UT, USA) were used for statistical analysis. Data was analyzed by using descriptive statistical methods (mean, standard deviation, median, frequency, ratio, range) and for comparing quantitative data Student t-test was used for two group comparisons of parameters with normal distribution, while Mann–Whitney U-test was used for two group comparisons of parameters without normal distribution. In the comparison of qualitative data Pearson chi-square test, Fisher–Freeman–Halton test, Fisher exact test, and Yates Continuity Correction test (Yates adjusted chi-square) were used. Spearman correlation analysis was used for the evaluation of the relation between parameters. Wilcoxon Signed Ranks test was used for within group comparison of parameters without normal distribution. Significance was evaluated in P<0.01 and P<0.05.
RESULTS
All of the patients who had ACL reconstruction with TT were male. Thirteen of these patients (48.1%) had left knee, and 14 of them (51.9%) had right knee ACL reconstruction surgery. The average age was 27.9±6.4 yr in TT group (range, 18–40 yr). Average time between ACL rupture and the time of surgery was 10.1 months (range, 1–36 months). The average follow-up period was 26.6 months (range, 12–42 months). Twenty-eight of the patients (96.4%) who had arthroscopic ACL reconstruction with AT were male and one (3.6%) was female. Fifteen of these patients (53.5%) had right knee, and 13 of them (46.5%) had left knee ACL reconstruction. The average age of the patients who had AT was 28.3±6 yr (range, 17–38 yr). Average time between ACL rupture and the time of surgery was 9.65 months (range, 1–36 months). The average follow-up period was 19.1 months (range, 9–36 months) (Tables 1, 2).
Table 1.
Variable | Transtibial (n=27) | Anatomic (n=28) |
---|---|---|
Age (yr) | 27.96±6.47 | 28.39±6.06 |
Follow-up duration (mo) | 27.11±9.02 | 19.21±7.41 |
Values are presented as mean±standard deviation.
Table 2.
Variable | No. (%) |
---|---|
Side | |
Left | 24 (43.6) |
Right | 31 (56.4) |
| |
Surgery technique | |
Transtibial | 27 (49.1) |
Anatomic | 28 (50.9) |
In TT group, the average duration to start postoperative sport activities was 6.37±1.96 months (range, 3–10 months), and the average duration to return to work was 1.89±0.58 months (range, 1–3 months) (Table 3). In the AT group, the average duration to start postoperative sport activities was 4.86±1.01 months (range, 3–7 months), and the average duration to return to work was 1.86±0.40 months (range, 1–3 months) (Table 3). There was a statistically difference between the two groups in duration of returning to sport. TT group had higher duration to return to sport (P<0.01) (Table 3). There was no difference between the two groups in duration of returning to work (P>0.05) (Table 3).
Table 3.
Variable | Thigh diameter difference (cm) | Duration (mo) | |
---|---|---|---|
| |||
Return to sport | Return to work | ||
Total | |||
Mean±SD | 1.33±1.32 | 5.60±1.72 | 1.87±0.49 |
Range | 0–4 | 3–10 | 1–3 |
Median | 1.00 | 5.00 | 2.00 |
| |||
Transtibial (n=27) | |||
Mean±SD | 1.89±1.40 | 6.37±1.96 | 1.89±0.58 |
Range | 0–4 | 3–10 | 1–3 |
Median | 2.00 | 6.00 | 2.00 |
| |||
Anatomic (n=28) | |||
Mean±SD | 0.79±0.99 | 4.86±1.01 | 1.86±0.40 |
Range | 0–4 | 3–7 | 1–3 |
Median | 0.50 | 5.00 | 2.00 |
| |||
P-value | 0.002** | 0.003** | 0.842 |
SD, standard deviation.
Mann–Whitney U-test.
P<0.01.
The average thigh difference was 1.89±1.40 cm and 0.79±0.99 cm in TT and AT, respectively. There was a statistically significant difference between the two groups. TT group had significantly higher values than AT group (P<0.01) (Table 3).
The TAS difference between preoperation and last follow-up in TT group was 1.81±3.16 points, and in AT group was 3.14±3.06 points. There was no difference in TAS between the two techniques at preoperation and at last follow-up (P>0.05). The increase of TAS in patients who had AT was higher than the patients who had TT (P>0.05) (Table 4).
Table 4.
Variable | Tegner | P-valueb) | Difference (point) | |
---|---|---|---|---|
|
|
|||
Preoperative | Postoperative | Preoperative & F/U | ||
Total | ||||
Mean±SD | 3.93±1.96 | 6.42±1.75 | 2.49±3.15 | |
Range | 1–9 | 3–9 | −4 to 8 | |
Median | 3.00 | 7.00 | 3.00 | |
| ||||
Transtibial (n=27) | ||||
Mean±SD | 4.33±2.11 | 6.15±1.63 | 1.81±3.16 | |
Range | 2–9 | 3–9 | 0.008** | −4 to 6 |
Median | 4.00 | 7.00 | 3.00 | |
| ||||
Anatomic (n=28) | ||||
Mean±SD | 3.54±1.75 | 6.68±1.85 | 3.14±3.06 | |
Range | 1–7 | 3–9 | 0.001** | −4 to 8 |
Median | 3.00 | 7.00 | 4.00 | |
| ||||
P-valuea) | 0.118 | 0.148 | 0.082 |
F/U, follow-up; SD, standard deviation.
Mann–Whitney U-test.
Wilcoxon signed ranks test.
P<0.01.
There was no difference in single-leg hop test at 55%–65%, 65%–75%, and 85%–95% level (P>0.05). In this test at 75%–85% TT group had higher values than AT group (P<0.05), AT group had higher values at 95%–105% level (P<0.05) (Table 5).
Table 5.
Single-leg hop test level | Transtibial (n=27) | Anatomic (n=28) | P-value |
---|---|---|---|
55%–65% | 2 (7.4) | 0 (0) | 0.236a) |
65%–75% | 5 (18.5) | 5 (17.9) | 1.000a) |
75%–85% | 6 (22.2) | 0 (0) | 0.010*, a) |
85%–95% | 9 (33.3) | 9 (32.1) | 1.000b) |
95%–105% | 5 (18.5) | 14 (50.0) | 0.030*, b) |
Values are presented as number (%).
Fisher exact test.
Yates continuity correction test.
P<0.05.
DISCUSSION
An ACL tear is a common injury, accounting for 40% to 50% of all ligamentous knee injuries, especially in young patients involved in sporting activities (Gianotti et al., 2009). Its incidence in the general population ranges from 1 in 3,500 patients in the United States to 34, 38, and 32 per 100,000 inhabitants in Norway, Denmark, and Sweden, respectively (Albright et al., 1999; Gordon and Steiner, 2004; Granan et al., 2009). At the University Hospital of the West Indies the first open procedure was done in 1994. By 1998 arthroscopic-assisted techniques were introduced and remain today as the gold standard.
The patient’s ability to return to a sport as well as the type of sport(s) played was documented. A sport was defined as all forms of physical activity which, through participation, aim at expressing or improving physical fitness and mental well-being, forming social relationships or obtaining results in competition at all levels (Council of Europe, 1993).
Reconstruction and rehabilitation rather than rehabilitation alone is more effective in achieving this goal (Kessler et al., 2008; Muaidi et al., 2007). Also by performing surgery the risk for further injury of the menisci and cartilage is decreased. Patients opting for rehabilitation alone have up to three year return to preinjury level (Noyes et al., 1983).
The definition of “return to sport” varies widely. A meta-analysis with 5,770 participants from 48 studies showed that, noted this definition referred to return-to-any-sport or return-to-preinjury level or return-to-competitive-sport (Ardern et al., 2011). Our show that most persons are able to return to sports after surgery, but are less likely to return to their preinjury level of participation in TT surgery group. We showed that TT group had lower values in term of the evaluation of activity after the surgery.
One of the major complaints of patients with chronic anterior cruciate-deficient knees is recurrent episodes of giving away and this causes significant restriction in players’ ability to perform sports that require many cutting and pivoting maneuvres (Noyes et al., 1983). As a result only 19%–82% of these athletes reported to return to their preinjury activity level and in some ended their sporting career (Myklebust et al., 2003; Roos et al., 1995). Rehabilitation alone is only supported in those patients who are willing to modify their activity level and avoid pivoting sports (Kostogiannis et al., 2008).
Several studies have extensively examined tunnel position in ACL reconstruction and found that inappropriate graft placement had significant adverse effect on graft incorporation and knee function (Ekdahl et al., 2009; Friedman and Feagin Jr, 1994; Morgan et al., 1995; Topliss and Webb, 2001; Van der Bracht et al., 2014). Conventional single-bundle ACL reconstruction with TT is widely used all over the world. Femoral tunnel created by transtibial approach will cause ACL to spread outside of the natural adhesion areas and lead to abnormal knee kinematics (Sinha et al., 2015; Steiner et al., 2009; Zantop et al., 2008). AT surgery technique provides better relocation of the graft in terms of kinematics of the knee. Therefore, this technique with combined good rehabilitation has better activity outcomes in terms of sport and regular life vs TT technique.
A clinical study concluded that the use of the anatomic replacement of the ACL resulted in greater knee stability and range of motion values and an earlier return to running compared to the TT (Alentorn-Geli et al., 2010).
It is shown that anatomical approach brought the tunnel layout to a more horizontal position and thus biomechanical studies have shown that in the coronal plane, it provides the anterior-posterior and the internal rotational stability better (Kilinc et al., 2016; Miller et al., 2011; Scopp et al., 2004; Seon et al., 2011).
We recommend surgery for young and active patients who feel instability in their daily activities and in their exercise capacity. The main aim is to bring activity level of patients who have ACL tear, close to or same to their preinjury level. Otherwise, patients with ACL tear determine an activity level according to their current state, reduce their previous activity levels. In our study, AT ACL reconstruction surgery results were better than the nonanatomic surgery results. By ensuring a better knee kinematics, patients increase their activity level, adaptation to the rehabilitation protocol, and the muscle strength. That should be considered to get remarkable outcomes with applied rehabilitation protocol also depending on surgery technique. Theoretically, anatomic reconstruction of the ACL can provide better knee kinematics and that provide better compliant to rehabilitation protocol. Anatomic ACL reconstruction will increase the better outcomes of patient rehabilitation in short and the long term.
Reconstruction of ACL is the management of choice for patients who sustain an ACL tear and wish to return to sports. Good-short and long-term knee outcome scores depend on rehabilitation protocol after surgery. Surgery technique should provide the adequate stability in rehabilitation period. Patients who had anatomic single-bundle ACL reconstruction obtain better adaptation and have better outcomes in rehabilitation.
Footnotes
CONFLICT OF INTEREST
No potential conflict of interest relevant to this article was reported.
REFERENCES
- Albright JC, Carpenter JE, Graf BK, Richmond JC. Knee and leg: soft tissue trauma. In: Beaty JH, editor. Orthopaedic knowledge update 6. Rosemont (IL): American Academy of Orthopaedic Surgeons; 1999. pp. 533–559. [Google Scholar]
- Alentorn-Geli E, Lajara F, Samitier G, Cugat R. The transtibial versus the anteromedial portal technique in the arthroscopic bone-patellar tendon-bone anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc. 2010;18:1013–1037. doi: 10.1007/s00167-009-0964-0. [DOI] [PubMed] [Google Scholar]
- Ardern CL, Webster KE, Taylor NF, Feller JA. Return to sport following anterior cruciate ligament reconstruction surgery: a systematic review and meta-analysis of the state of play. Br J Sports Med. 2011;45:596–606. doi: 10.1136/bjsm.2010.076364. [DOI] [PubMed] [Google Scholar]
- Arendt E, Dick R. Knee injury patterns among men and women in collegiate basketball and soccer. NCAA data and review of literature. Am J Sports Med. 1995;23:694–701. doi: 10.1177/036354659502300611. [DOI] [PubMed] [Google Scholar]
- Council of Europe. The European sports charter: Brussels: Council of Europe; 1993. [Google Scholar]
- Ekdahl M, Nozaki M, Ferretti M, Tsai A, Smolinski P, Fu FH. The effect of tunnel placement on bone-tendon healing in anterior cruciate ligament reconstruction in a goat model. Am J Sports Med. 2009;37:1522–1530. doi: 10.1177/0363546509332503. [DOI] [PubMed] [Google Scholar]
- Friedman RL, Feagin JA., Jr Topographical anatomy of the intercondylar roof. A pilot study. Clin Orthop Relat Res. 1994;(306):163–170. [PubMed] [Google Scholar]
- Gianotti SM, Marshall SW, Hume PA, Bunt L. Incidence of anterior cruciate ligament injury and other knee ligament injuries: a national population-based study. J Sci Med Sport. 2009;12:622–627. doi: 10.1016/j.jsams.2008.07.005. [DOI] [PubMed] [Google Scholar]
- Gordon MD, Steiner ME. Anterior cruciate ligament injuries. In: Garrick JE, editor. Orthopaedic knowledge update sports medicine. 3rd ed. Rosemont (IL): American Academy of Orthopaedic Surgeons; 2004. pp. 169–170. [Google Scholar]
- Granan LP, Forssblad M, Lind M, Engebretsen L. The Scandinavian ACL registries 2004–2007: baseline epidemiology. Acta Orthop. 2009;80:563–567. doi: 10.3109/17453670903350107. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hurd WJ, Axe MJ, Snyder-Mackler L. Influence of age, gender, and injury mechanism on the development of dynamic knee stability after acute ACL rupture. J Orthop Sports Phys Ther. 2008;38:36–41. doi: 10.2519/jospt.2008.2609. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hutchinson MR, Ireland ML. Knee injuries in female athletes. Sports Med. 1995;19:288–302. doi: 10.2165/00007256-199519040-00006. [DOI] [PubMed] [Google Scholar]
- Ireland ML. Anterior cruciate ligament injury in female athletes: epidemiology. J Athl Train. 1999;34:150–154. [PMC free article] [PubMed] [Google Scholar]
- Kessler MA, Behrend H, Henz S, Stutz G, Rukavina A, Kuster MS. Function, osteoarthritis and activity after ACL-rupture: 11 years follow-up results of conservative versus reconstructive treatment. Knee Surg Sports Traumatol Arthrosc. 2008;16:442–448. doi: 10.1007/s00167-008-0498-x. [DOI] [PubMed] [Google Scholar]
- Kilinc BE, Kara A, Oc Y, Celik H, Camur S, Bilgin E, Erten YT, Sahinkaya T, Eren OT. Transtibial vs anatomical single bundle technique for anterior cruciate ligament reconstruction: a retrospective cohort study. Int J Surg. 2016;29:62–69. doi: 10.1016/j.ijsu.2016.03.025. [DOI] [PubMed] [Google Scholar]
- Kostogiannis I, Ageberg E, Neuman P, Dahlberg LE, Fridén T, Roos H. Clinically assessed knee joint laxity as a predictor for reconstruction after an anterior cruciate ligament injury: a prospective study of 100 patients treated with activity modification and rehabilitation. Am J Sports Med. 2008;36:1528–1533. doi: 10.1177/0363546508317717. [DOI] [PubMed] [Google Scholar]
- Miller CD, Gerdeman AC, Hart JM, Bennett CG, Golish SR, Gaskin C, Miller MD. A comparison of 2 drilling techniques on the femoral tunnel for anterior cruciate ligament reconstruction. Arthroscopy. 2011;27:372–379. doi: 10.1016/j.arthro.2010.08.012. [DOI] [PubMed] [Google Scholar]
- Morgan CD, Kalman VR, Grawl DM. Definitive landmarks for reproducible tibial tunnel placement in anterior cruciate ligament reconstruction. Arthroscopy. 1995;11:275–288. doi: 10.1016/0749-8063(95)90003-9. [DOI] [PubMed] [Google Scholar]
- Muaidi QI, Nicholson LL, Refshauge KM, Herbert RD, Maher CG. Prognosis of conservatively managed anterior cruciate ligament injury: a systematic review. Sports Med. 2007;37:703–716. doi: 10.2165/00007256-200737080-00004. [DOI] [PubMed] [Google Scholar]
- Myklebust G, Holm I, Maehlum S, Engebretsen L, Bahr R. Clinical, functional, and radiologic outcome in team handball players 6 to 11 years after anterior cruciate ligament injury: a follow-up study. Am J Sports Med. 2003;31:981–989. doi: 10.1177/03635465030310063901. [DOI] [PubMed] [Google Scholar]
- Noyes FR, Mooar PA, Matthews DS, Butler DL. The symptomatic anterior cruciate-deficient knee. Part I: the long-term functional disability in athletically active individuals. J Bone Joint Surg Am. 1983;65:154–162. doi: 10.2106/00004623-198365020-00003. [DOI] [PubMed] [Google Scholar]
- Prodromos CC, Han Y, Rogowski J, Joyce B, Shi K. A meta-analysis of the incidence of anterior cruciate ligament tears as a function of gender, sport, and a knee injury-reduction regimen. Arthroscopy. 2007;23:1320–1325.e6. doi: 10.1016/j.arthro.2007.07.003. [DOI] [PubMed] [Google Scholar]
- Roos H, Ornell M, Gärdsell P, Lohmander LS, Lindstrand A. Soccer after anterior cruciate ligament injury--an incompatible combination? A national survey of incidence and risk factors and a 7-year follow-up of 310 players. Acta Orthop Scand. 1995;66:107–112. doi: 10.3109/17453679508995501. [DOI] [PubMed] [Google Scholar]
- Scopp JM, Jasper LE, Belkoff SM, Moorman CT., 3rd The effect of oblique femoral tunnel placement on rotational constraint of the knee reconstructed using patellar tendon autografts. Arthroscopy. 2004;20:294–299. doi: 10.1016/j.arthro.2004.01.001. [DOI] [PubMed] [Google Scholar]
- Seon JK, Park SJ, Lee KB, Seo HY, Kim MS, Song EK. In vivo stability and clinical comparison of anterior cruciate ligament reconstruction using low or high femoral tunnel positions. Am J Sports Med. 2011;39:127–133. doi: 10.1177/0363546510377417. [DOI] [PubMed] [Google Scholar]
- Sinha S, Naik AK, Arya CS, Arya RK, Jain VK, Upadhyay G. Transtibial guide wire placement for femoral tunnel in single bundle anterior cruciate ligament reconstruction. Indian J Orthop. 2015;49:352–356. doi: 10.4103/0019-5413.156224. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Steiner ME, Battaglia TC, Heming JF, Rand JD, Festa A, Baria M. Independent drilling outperforms conventional transtibial drilling in anterior cruciate ligament reconstruction. Am J Sports Med. 2009;37:1912–1919. doi: 10.1177/0363546509340407. [DOI] [PubMed] [Google Scholar]
- Topliss C, Webb J. An audit of tunnel position in anterior cruciate ligament reconstruction. Knee. 2001;8:59–63. doi: 10.1016/s0968-0160(01)00067-9. [DOI] [PubMed] [Google Scholar]
- Van der Bracht H, Verhelst L, Stuyts B, Page B, Bellemans J, Verdonk P. Anatomic single-bundle ACL surgery: consequences of tibial tunnel diameter and drill-guide angle on tibial footprint coverage. Knee Surg Sports Traumatol Arthrosc. 2014;22:1030–1039. doi: 10.1007/s00167-013-2416-0. [DOI] [PubMed] [Google Scholar]
- Woo SL, Wu C, Dede O, Vercillo F, Noorani S. Biomechanics and anterior cruciate ligament reconstruction. J Orthop Surg Res. 2006;1:2. doi: 10.1186/1749-799X-1-2. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Zantop T, Diermann N, Schumacher T, Schanz S, Fu FH, Petersen W. Anatomical and nonanatomical double-bundle anterior cruciate ligament reconstruction: importance of femoral tunnel location on knee kinematics. Am J Sports Med. 2008;36:678–685. doi: 10.1177/0363546508314414. [DOI] [PubMed] [Google Scholar]